The goal of this clinical trial is to evaluate whether the LasaiON program, which combines transcutaneous auricular vagus nerve stimulation (taVNS) with breathing supported by heart rate variability biofeedback (HRV-B; emWave), reduces emotional distress and improves stress-regulation processes in adults. The study will also assess the safety, tolerability, and feasibility of the intervention.
The main questions it aims to answer are:
1. Does the LasaiON program reduce emotional distress in adults?
2. What physiological, psychological, and verbal-cognitive changes are observed following the intervention?
3. What discomforts, adverse effects, or tolerability issues do participants experience during the program?
Researchers will use a prospective 2 × 2 factorial randomized controlled design to examine the effects of stimulation condition (active taVNS vs. sham taVNS) and training condition (active HRV-biofeedback vs. control training), as well as their potential interaction. Participants will be randomly allocated in equal proportions (1:1:1:1) to one of four groups: sham taVNS + control training, sham taVNS + HRV-biofeedback, active taVNS + control training, or active taVNS + HRV-biofeedback.
Participants will:
* undergo baseline assessments on Day 1 before the intervention;
* complete 5 consecutive daily 60-minute sessions according to group allocation;
* undergo post-intervention assessments on Day 5 after the final session;
* complete psychometric, physiological, and verbal-cognitive assessments, including STAI, HAM-D, WHO-5, EEG, skin conductance, startle response, heart rate variability measures derived using Kubios HRV Premium, and daily five-word reports with valence ratings analyzed using IRaMuTeQ;
* have adherence and tolerability recorded at each session using a checklist.